xDrip » Features » Display » Glucose range
You can adjust the glucose range shown on screen as long as no readings fall outside that range. If a reading exceeds the configured limits, the graph will automatically pan to keep the latest readings visible.
You can access this setting at:
Settings −> xDrip+ Display Settings −> Graph Settings −> Customize y axis range

Enable the feature. When enabled, two additional settings on the same page become available, allowing you to adjust Y Min and Y Max.
Changes take effect immediately on the graph.
If you later disable the feature, the graph returns to the default range, but your custom values are not erased. Re-enabling the feature restores the previously selected settings.
The following image shows the exact same readings displayed at the two extremes of the Y-axis range.

If you significantly reduce the range and a high reading occurs, xDrip will automatically pan the graph to show the latest readings.
This automatic panning lasts for up to 3 hours, or as long as high readings persist. If this happens frequently, consider using a wider range to avoid repeated panning.